In today's copper access network, a customers' achievable physical layer rate depends on the characteristics of the direct link from its terminal unit at remote end to its terminal unit at operator end, which in turn depends on the quality and length of the copper loop, the available frequency bands, line noise, etc. In an access system based on XDSL technologies, an XDSL Terminal Unit at remote end is referred to as XTU-R, and a terminal unit at operator end is referred to as XTU-O which is generally located at a central office, exchange, intermediate cabinet or Optical Network Unit, i.e. at operator end of the loop. Typically, the customers connected to the Central Offices (COs)/cabinets on longer copper loops get lower rates than those connected on shorter ones. As such, the bandwidth and services that may be offered to the customers on longer loops are limited due to the lower available rates.
In order to overcome the limitations of longer copper loops, today's network operators deploy fiber to cabinets in proximity of customers (generically called “FTTX” or “Fiber to the X”, where X could refer to premises (FTTP), curb (FTTC), drop-point (FTTD), etc.). Depending on the choice of the FTTX technology used, the copper loop is shortened or completely eliminated (as in FTTP). Although these fiber connection techniques improve the rates of the customers connected on shorter copper loops, they do not help the legacy customers still on the longer copper loops.